Pavement markings convey information to drivers and pedestrians by providing exposed visible, reflective and/or tactile surfaces that serve as indicia upon a traffic surface. In the past such a function was typically accomplished by painting a traffic surface. Modern pavement marking materials offer significant advantages over paint such as dramatically increased visibility and/or retro reflectance, improved durability, and temporary removable marking options. Examples of modern pavement marking materials are thermoplastic, preformed pavement marking sheet materials, tapes and raised pavement markers.
Signage in many cases is shipped to the job site as articles of the whole, depicting specific information or a visual theme and requiring assembly of the articles into the desired pattern. Assembly steps, without sequential assembly indicators, consume time and effort and pose a risk that the completed signage may be incorrect after adhesion to the pavement surface.
The thermoplastic signage may be hydrocarbon or alkyd based and includes a hot melt thermoplastic application. Thermoplastic signage must meet the standard specifications as published in the AASHTO—American Association of State Highway Transportation Officials). Designation: M 249-98
Traffic surfaces include areas for pedestrians, motorized vehicles, aircraft, human powered conveyances, programmable robotics and may be horizontal or vertical.
In recent years increasing numbers of municipalities, office complexes, shopping centers and other commercial developments have utilized thermoplastic pavement markings with various patterns and designs to guide, decorate and protect high traffic areas such as highways, pedestrian crosswalks, parking lots and business entrances. A typical, conventional pavement marking pattern as set forth in PCT application US/03/03156 (WO 03/064771 A1) consists of a preformed planar thermoplastic sheet or strip having a thickness of approximately 0.01″ (2.5 mm). The widths of these patterns vary with the purpose of the marking Such patterns may include a first section or grid, for example to represent the mortar joints in a “brick” design and a plurality of second sections or “bricks” which are coplanar therewith, usually in a color different from the mortar color. The second section or bricks which are separately manufactured are inserted into the first section or grid before application of the pattern to the pavement. Various such two section marking patterns are commonly available such as: herringbone, standard brick, cobblestone, paving slabs and many other designs (which are constantly evolving). Marking patterns with more than two sections are also commonly available such as horizontal highway and street signage, logos and many others.
As hereinbefore mentioned, these marking patterns consist of two or more independent sections which must be carefully assembled and handled before applying to pavements such as asphalt, concrete or other suitable substrates. These marking patterns are placed at desired locations such as road crosswalks, intersections, parking lots or other sites. In some cases heat is then applied to soften the pavement marking pattern causing it to firmly adhere to the substrate. Various adhesives can also be used to adhere the marking pattern to the substrate.
While the purchase of such pavement marking patterns is relatively inexpensive, much time and labor is devoted to the assembly and application of the pattern to the substrate. Most patterns consist of two or more sections which are independently formed for manual assembly at the job site and time and effort is needed to assemble and maintain the integrity of a pattern before the heat treatment. Usually the pattern placed on the substrate must be moved manually for adjustment purposes. During such movement, the independent sections in the pattern inadvertently become unaligned, requiring reinsertion or realignment. If the realignment is not precisely accomplished, the marking pattern will have lost its integrity and the entire pattern must be removed manually from the substrate, the substrate cleaned and a second attempt at the application made with the reinserted or new marking pattern. This re-application results in extra time, labor and materials. In the past, to maintain the integrity of the marking pattern before the heat treatment and during the handling and placement, “spot adhesives” have been used which remain somewhat “tacky” after being applied to the bottom of the patterns at the grid intersections to maintain pattern integrity. However, these small adhesive circles or “spots” are generally a different type of polymer than the marking pattern and can prevent proper attachment and easy movement of the marking pattern on the substrate at the spot adhesive locations before and during the heat application of the marking Also, certain spot adhesives are not compatible with the plastic materials from which the patterns are formed and can cause the pavement marking sections to separate from the substrate after the heat application, as only a weak bond is formed with the substrate.
Specifically, the standard for thermoplastic marking bond strength can be found in ASTM D4796, which states the test method and bonding strength of thermoplastic signage to concrete as: Bond Strength—After heating the thermoplastic material for four hours at 425 degrees F. the bond strength to Portland Cement Concrete shall exceed 1.24 Mpa (˜180 psi). Preferably the bond strength is from about 200 psi to about 500 psi.
Thermoplastic signage must reach a softening point within a range of about 400 degrees F. to about 450 degrees F. as determined by the ring and ball softening point test method specified in AASHTO Designation: M 249, section 12 in order to properly adhere to most pavement surfaces.
Alkyd resins are the reaction product of an oil or fatty acid, polyol(s) and polyacids. Alkyds can also be modified or co-reacted with many other material types (rosin, phenolic, urethane, vinyl monomers etc.). The precise combination of the many possible ingredients, together with careful control of the reaction, influences the final properties of the alkyd produced.